Automatic test equipment (ATE) for integrated circuits (ICs) has been developed to facilitate electrical testing of IC's at selected stages of the IC manufacturing process. Such ATE often includes a test head which must be manipulated into a docked position with a testing peripheral using a test head positioner (or manipulator). Test head positioners are generally described, for example, in U.S. Pat. Nos. 7,276,894, 7,245,118, 6,911,816, 6,888,343, 5,608,334, 5,450,766, 5,030,869, 4,893,074, 4,715,574, 4,705,447 and 4,527,942, and WIPO publications WO 05015245A2, WO 2008137182A2 and WO 04031782A1. All of the foregoing are incorporated by reference in their entirety for their teachings in the field of test head positioners for automatic test equipment for integrated circuits or other electronic devices.
Briefly, a conventional automatic testing system generally includes a peripheral apparatus for precisely placing and constraining the IC device under test (DUT) in a fixed position test site. Also included is a moveable test head for testing the DUT. The peripheral apparatus may, for example, be a wafer prober for testing devices before they are separated from a silicon wafer or a package handler for positioning and testing packaged devices. In practice, the test head is translated and/or rotated about one or more axes and brought into the vicinity of the DUT test site included in the peripheral apparatus. Prior to docking, the mating connectors of the test head and the DUT test site are precisely aligned to avoid damaging any of the fragile electrical and mechanical components. Once docked, test electronics of the test head transmit signals through various contacts of the DUT and execute particular test procedures within the DUT. In the course of testing, the test head receives output signals from the DUT, which are indicative of its electrical characteristics.
In order to precisely mate the test head with the peripheral apparatus, the test head is optionally capable of movement with all six degrees of spatial freedom. To facilitate such motion, a test head positioner system is commonly employed to precisely position the test head with respect to the peripheral. The test head positioner system may also be referred to in the art as a test head positioner or a test head manipulator.
Referring now to the exemplary test head positioner described in U.S. Pat. No. 6,888,343, the test head 502 is coupled to main arm 511, and main arm 511 is slideably coupled to linear guide rail 510 that extends vertically along the length of column 545, as best shown in FIGS. 5A and 5B. A motor 2416 may be adapted to translate main arm 511 (and test head 502) vertically along linear guide rail 510. A counter weight assembly biases the weight of main arm 511 (and test head 502) in a substantially fixed vertical position upon disengagement of the motor. As best shown in FIGS. 23 and 24, motor 2416 is mounted to frame 2422 of column 545, and is indirectly connected to pulley 2421 by timing belt 2420. Pulley 2421 is mounted to pulley 2406 by fasteners 2407 (shown in FIG. 23, but not numbered), such that pulleys 2421 and 2406 rotate simultaneously. A cable 2410 is positioned about pulley 2421. One end of cable 2410 is coupled to mount 736 of main arm 511 and the opposing end of cable 2410 is coupled to a counter balance 2413. In operation, if clutch 2426 of motor 2416 is engaged, the motor 2416 rotates pulleys 2406 and 2421, thereby translating the end of cable 2410 that is connected to mount 736 along the Y-axis. Thus, the cable 2410 translates the mount 736 of main arm 511, along with test head 502, in a vertical direction. Once clutch 2426 of motor 2416 is disengaged, the counterbalance 2413 suspends mount 736 and test head 502, in a substantially fixed vertical position. Furthermore, with clutch 2426 of motor 2416 disengaged, test head 502 is in a substantially weightless condition and may be readily moved vertically with a relatively small externally (manually) applied force. This is known as compliance and it enables an operator to manually position the test head or a docking apparatus to maneuver the test head into or out of its docked position with a peripheral. A second embodiment of this scheme is described in U.S. patent application Ser. No. 12/405,547, which is presently unpublished. However, this arrangement: 1) requires volume within the top portion of the column, which may reduce the overall vertical stroke for a column of a given height; 2) may require relatively costly coupling components; 3) does not limit the range of compliant motion; and 4) does not provide any means to detect interference when driving the load into position. An object of the present invention is to provide a mechanism to drive the balanced load and allow compliant motion in a manner that overcomes one or more of these effects.
Further, the exemplary test head positioners disclosed in WO 05015245A2, WO 04031782A1, and U.S. Pat. No. 4,705,447 each support a test head in a substantially-weightless, compliant condition using a pneumatic apparatus rather than counter weights. In WO 05015245A2 and WO 04031782A1, a pneumatic controller is provided which, in addition to providing compliance, automates vertical translation of the test head.
The aforementioned test head positioner systems may be sufficient; nevertheless, there continues to be a need to further improve vertical support systems for test heads, in the interest of weight, efficiency, simplicity and cost. Further, in the aforementioned test head positioner systems, the range of compliant vertical motion is limited only by the full stroke of vertical motion available in the positioner. In some applications it may be preferable to have compliant motion limited to a comparatively small range.